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By Joe Brock

JOHANNESBURG (Reuters) - Major private equity firms have seen a number of top management departures in Africa, individuals familiar with the matter said, as the funds grapple with investments hurt by a weak economy.

U.S. firm Carlyle (NASDAQ: CG), Standard Chartered (NASDAQ: STAN) and emerging market-focused Actis have all seen a change of top executives at their Africa funds, according to these six individuals.

Once seen as a beacon of growth, private equity firms expanded their business in the region just before the financial crash. A weak economy and falling currencies have now taken the gloss off a decade of 'Africa rising' optimism.

Some investments by these companies have struggled in the downturn. The changes at these groups, which pool the money of pension funds and international investors to buy, say, a stake in local companies, bring this decline into focus.

Carlyle's Africa chief, Marlon Chigwende, confirmed that he had left. His departure in August followed a number of unsuccessful buyouts, including in Nigeria's struggling Diamond Bank , two sources familiar with the matter said.

Chigwende told Reuters that investments had done well while he was in charge and that he was now setting up his own fund. Carlyle did not comment on the reasons for his departure.

The Africa chief for Actis, John van Wyk, is also due to leave, two sources familiar with the matter said, asking to remain anonymous because of the sensitivity of the matter. Van Wyk did not respond to a request for comment.

The company's global private equity head Peter Schmid, a veteran of African fund management, said he too would be leaving the group. An Actis spokesman declined to comment.

Standard Chartered is parting ways with its Africa head, Peter Baird, as part of a plan to reduce its Africa team from 11 members to five, two industry sources said.

Standard Chartered's private equity head, Joe Stevens, confirmed that the team was being "streamlined" but said it was not linked to performance.

A confidential investor prospectus, seen by Reuters, shows that Chigwende and two fund managers leaving Standard Chartered, Adrian Smith and Mayowa Ayodele, are planning to launch Arkana Partners, a new African private equity firm.

Smith and Ayodele declined to comment.

DRY UP

The changes come as a slump in oil has hit Africa hard, pushing countries such as South Africa, Nigeria and Angola into or close to recession and sending their currencies tumbling.

This change of fortune is reflected in the private equity sector.

African private equity deals fell to $2.5 billion last year, compared with $8.1 billion in 2014, and fundraising is expected to drop this year, the African Private Equity and Venture Capital Association said.

Many of the hardest hit investments have been in Nigeria, where subdued oil prices have pushed Africa's most populous country and biggest economy into recession.

That has seen the supply of dollars dry up and the local Naira currency weaken, cutting the value of foreign investments in the country.

Standard Chartered's investments include Nigeria's Union Bank (NYSE: UBN), which has halved in value this year.

Both Actis and Carlyle have suffered significant losses from stakes in Nigeria's Diamond Bank .

Actis invested $134 million in Diamond Bank in 2007 and sold its stake in 2014 for an undisclosed amount, during which time the shares fell around 60 percent.

Diamond's Bank stock has slumped a further 90 percent in dollar terms since Carlyle invested $147 million in 2014.

Diamond Bank has been hammered by a shrinking economy, a plunging currency and acute foreign exchange shortages, all a consequence of the slump in the oil price.

Carlyle also bought into J&J Transport and Traxys between 2013 and 2014. J&J is an African transport firm with mining customers, while Traxys trades commodities in Africa and provides logistics for that sector.

Both have been hit by the slump in commodity prices since the private equity firms bought their stakes, two people familiar with the matter said.

An Actis spokesman declined to comment on fund performance, adding that it had worked with Diamond Bank through "a period of considerable volatility to build a strong franchise".

The downturn is in stark contrast to the region's earlier rapid growth, spurred by a commodity boom, debt forgiveness extended by rich nations to some African countries and the spread of mobile phones.

Some in the industry, however, still see potential.

"With the exception of Diamond Bank, the portfolio is performing in line with expectations," Eric Kump, co-head of Carlyle's Africa fund and Chigwende's successor, told Reuters.